Glossmeter

ABSTRACT

A glossmeter for the determination of the gloss of regular and irregular shaped objects, including objects with curved surfaces. Illumination is at any desired angle of incidence on the object, which angle can be varied at will. Photosensitive elements (15) are provided in an array arranged on an arc (14), which elements face the objects and which receive light reflected and scattered by the objects. Suitable objects are various kinds of fruit, vegetables, rice and any other object where exact surface gloss is of importance.

FIELD OF THE INVENTION

The invention relates to a novel gloss-meter which provides detailedinformation on the gloss of a given object. It allows measurements whichprovide detailed Information as regards the entire surface of theobject. Amongst others, the novel gloss meter can be used fordetermining the gloss of irregular objects and also of curved ones.

BACKGROUND OF THE INVENTION

Gloss is a surface attribute causing a shiny or lustrous appearance. Itis generally associated with specular reflection by the object. However,specular reflection can vary from one surface to another as follows:

1. The fraction of light reflected in the specular direction.

2. The manner and extent to which light is spread to either side of thisspecular direction.

3. The change of fractional reflectance as specular angle changes.

There are at least six different visual criteria by which glossiness isranked (Table 1).

ESTABLISHED METHODS OF MEASURING GLOSS

There exist a variety of methods to measure gloss since differentaspects of reflection, need to be measured to duplicate, as closely aspossible, the different visual gloss-grading parameters.

The first established method for gloss measurement (Ingersoll, 193.4)was based on the principle that light is polarized in specularreflection, whereas diffusely reflected light, is nonpolarized. TheIngersoll glarimeter had a specular geometry, with incident and viewingangles at 57.5. Gloss was evaluated by a contrast method that, with theuse of a polarizing element, "substracted" the specular component fromtotal reflection.

In around 1930, Pfund pointed out that although specular shininess isthe basic (objective) evidence of gloss, actual surface glossyappearance (subjective) relates to the contrast between specularshininess and the diffuse light of the surrounding surface area (nowcalled "contrast gloss" or "luster"). If black and white surfaces of thesame shininess are visually compared, the black will appear glossierbecause of the greater contrast between the specular highlight and theblack surroundings as compared to that with than white surroundings.Pfund was the first to suggest that more than one method is needed toanalyze gloss (Pfund, 1930).

In his investigation of gloss in the early 1930s Hunter used a specularangle of 45°, as did the first photoelectric gloss methods.

But visual evaluation of a large number of samples (primarily paint)eventually demonstrated that the 60° angle provided the best overallestimates (Hunter and Judd, 1939). The 60° method suggested in 1939 wassubsequently adopted by the American Society for Testing and Materials(ASTM Method D523). It is widely used for paints, plastics, waxes andfloor coverings, and is more widely used than any other gloss testprocedure. The old 45° method is now used primarily for glazed ceramicsand polyethylene and other plastic films.

Incorporated into ASTM Method D523 in 1951 as alternative procedureswere a 20 specular test for evaluating high-gloss finishes, developedearlier at the duPont Company (Horning and Morse, 1947) and an 85°method for evaluating low-gloss, matte surfaces. The latter sheen methodwas developed in 1938 by J. W. Ayers of the C. K. Williams Company(Ayers, 1938; Hunter, 1952) and was subsequently used to test mattecamouflage finishes used by the Ordinance Department. It is now used formeasuring flat Interior wall paints, and low-gloss exterior paintedaluminum siding.

A two-parameter method for 60° specular gloss designed to distinguishthe image-forming gloss surface of nonmetals from nonimage-forming glosssurfaces was adopted as ASTM Method D1471 in 1969 (Nimeroff, 1957). Itwas designed to cover those cases in which measurements made by the ASTMMethod D523 60 gloss method did not correlate with gloss appearance.Method D1471 specifies a second, two-receiver aperture, to be used inconjunction with the aperture of Method D523. An evaluation is then madeof the amount of light received by each of the apertures.

In 1937, th e paper industry adopted a 75° specular-gloss method becausethe angle gave the best separation of coated book papers (Institute ofPaper Chemistry, 1937; Hunter 1958). This method was adopted in 1951 bythe Technical Association of Pulp and Paper industries as TAPPI MethodT480. For the evaluation of waxed, lacquered, and cast-coated high-glosspapers at 20°, TAPPI Method T653 was adopted in 1958 with window angularsizes different from those of the 20 ASTM paint method (Hunter andLofland, 1956).

SUMMARY OF THE INVENTION

Conventional gloss-meters and gloss-measurements suffer from a number ofinherent drawbacks. Amongst these there may be mentioned the highresolving power of the human eye, compared with that of most reflectancemeasuring means. Most existing instruments provide scanty reliableinformation on the gloss of curved objects. The novel gloss-meterovercomes to a large extent the drawbacks of conventional instruments.

According to the present invention there is provided a versatilegloss-meter which is suitable for measuring gloss of flat as well ascurved surfaces and bodies. Examples of produce the gloss of which canbe determined in an objective manner, are fruit and certain types ofvegetables.

The novel instrument is based on specific illumination means, whichallows to change the angle of the light beam incident on the objectduring measurement.

Furthermore, means are provided for obtaining exact values of lightreflected by the object and scattered by same over a wide solid angle.Means are also provided for scanning effectively a wide range of spatialangle for reflected and scattered light. Last not least, means areprovided for the rapid and exact evaluation of the measured parameters,giving a quantititive indication of the gloss of the measured object andif desired, of other parameters of such an object. A variety of lightsources can be used for creating the light beam by which the object isilluminated. According to preferred embodiment a narrow monochromaticlight beam, such as from a suitable laser, is used for illumination.

Scattered and reflected light reaches an array of photosensitiveelements, preferably arranged on an arc or part of arc, at a certaindistance from the object, so that the photosensitive elements are atabout the same distance from the measured object.

Increased sensitivity and capability of spatial resolution results fromthe use of a large number of such elements, each of a rather smallsurface area. Instead of such an array there may be used a video camera,preferably arranged in a movable manner so as to be able to scan a largespatial angle.

According to another embodiment, the object can be illuminated from acertain angle of incidence, and light coming from it can be collected ona half-transparent screen, which can be scanned so as to determine lightintensity distribution over its surface. According to one embodiment ofthe invention, there are used two arrays of photo-sensitive elements,such as photodiodes or the like, which are arranged on two arcs, onepreferably in the reflection plane and the other at 90° thereto, also onan arc. Generally the maximum of light intensity is found somewhere onthe first arc, and this value can be taken as reference point for thecalculation of gloss, obtained by dividing such maximum value by thediscrete values at different points of the arc.

The measurement of gloss can be effected using a number of alternatives:

1. The object is stationary, generally in a suitable shallow hole, it isilluminated by a light source (generally a laser beam), whichilluminates the object either at a given angle, or the angle ofillumination which can be varied from horizontal to 90° elevation. Thereare provided two arches which support a large number of photosensitiveelements, and which receive the light reflected or scattered from theobject. The arches are stationary.

2. There can be provided a system where the illumination is either at agiven angle, or which can be varied as regards angle with the horizontalplane, while illuminates the object,there is provided a system where theangle of the beam of light incident on the object can be varied.

3. An array of photosensitive elements can be arranged on aquarter-arch; this can be moved in a plane vertical to the supportsurface so as to scan any desired angle; generally a quarter of thecircle, i.e. 90° will be sufficient.

The measurement can be made with a stationary light source at a givenelevation; or measurements can be repeated with the light source atdifferent angles.

4. There can be arranged a translucent screen above the object, whichwill generally be flat, the light source is used to illuminate theobject at one or more angles of elevation, and there results an unevenillumination of the translucent screen, which is scanned by means of aCCD or similar means.

5. An array of photosensitive elements can be arranged in one or morearches; a source of a light beam can be provided either at a fixedelevation or at elevations which can be changed to predetermined values;the object is arranged on a rotatable support, so that when this rotatesthe entire visible surface of the object will be illuminated and lightcoming from its surface will be evaluated.

DESCRIPTION OF PREFERRED EMBODIMENT

A number of alternative embodiments of the invention are illustratedwith reference to the enclosed schematical Figures, which are notaccording to scale, and in which:

FIG. 1 is a perspective view of one glossmeter of the invention;

FIG. 2 is a perspective view of another embodiment of the invention.

FIG. 3 is a graph of light scattering recorded by the glossmeter.

As shown in FIG. 1, the glossmeter illustrated comprises in combinationa supporting plate 11, with a central recess 12 which serves to hold thebody to be examined. Around plate 11 there is provided a rail-likestructure 13 which supports arch 14, at the inside of which, facingrecess 12, there are provided a plurality of photosensitive elements 15,such as photodiodes or the like, which are connected via cable 16 toamplifier 17 and to evaluation means 18. There is provided a second arch19, on which there is slidingly arranged a light source 20, such as alaser with optical system to provide a light beam, directed at theobject at the center of the plate 11. Two positions of the light source20 are shown, 20 and 20'. The light source can be moved so as to makewith the surface of support 11 an angle from above 0° to 90°. This lightsource is connected with flexible cable 21 connected with power source22.

A device of this type can be used with a stationary arch 14 and in thiscase the photoelements will register the light coming from the object atthe center of the plate 11.

The embodiment where the arch 14 can be moved along the perimeter of theplate 11 has the advantage that the light coming from various parts ofthe surface of the object is evaluated. Another possible embodiment, notshown, is an arrangement where there is provided at the center of theplate 11, a rotatable support, which can be rotated with the objectsupported by it, so as to scan the surface of the object.

Another embodiment is illustrated in FIG. 2, which comprises incombination a support plate 31, provided at its center with a rotatablesupport 32, which supports the object which is to be examined. There areprovided two arches, 33 and 34, at the interior surface of which, facingthe object, there are provided a plurality of photosensors, such asphotodiodes 35. There is provided another arch 36, which supports thelight source 37, which emits a beam directed at the object. This isadvantageously a laser, and this is arranged on said arch 36 so as tomake different angles with the surface of the plate 31. The rotatingobject and the variable-angle laser beam enable a thorough illuminationof the surface of the object and a thorough evaluation of the gloss ofthe object.

The laser 37 is connected via cable 38 to power source 39 and the outputof photosensors 35 passes via cable 40 to amplifying means 41, which isconnected with evaluation means 42.

EXAMPLE 1

Ripe tomatos, of the Rehovot 175 strain, were placed in the glossmeterof the invention, and illuminated by a light beam from a helium-neonlaser, at an angle of 45° with the horizontal supporting plate. Thelight was reflected on a translucent polypropylene screen arrangedparallel to the supporting plate, and at an adequate distance from this.The light signals were picked up by an array of image analyzers by meansof a suitable video-computer card, and the data were processed by a486-IBM compatible computer. The results call be obtained in a graph ofarbitrary relative values, as shown in enclosed FIG. 3 against lightscattering in mm. The enclosed graph is that obtained with a certainspecific tomato.

The picture is evaluated by two routes by measuring the fit with adistribution curve and determination of the relevant parameters, as wellas by establishing a numerical value which characterizes a certainexamined item. Every item, sucti as fruit, vegetable or the like, has tobe tested in various positions, at least six, with one from each side,so as to obtain a more representative value as to its overall gloss.

The glossmeter according to the present invention was used to measurecurved surfaces of Dwarf Cavendish Bananas. It was found that theripening of the bananas was accompanied by a gradual decrease in gloss,which also correlated well with certain chemical and physical changes inthe bananas. The change of gloss correlated well with changes of peelcolor and thus can be used to evaluate ripeness of bananas. Theillumination was by a helium-neon laser light beam.

The angle of incidence of the laser beam on the banana peel was 45°.

Further experiments were carried out with eggplants, mature greentomatoes and apples. The average readings with the novel glossmeter were9.5, 7.4 and 6.3 arbitrary GU units from eggplants, tomatoes and apples,respectively.

EXAMPLE 2

Commercially mature apples of the cultivar "Granny Smith" were obtainedfrom a local orchard. All tests were undertaken within 2 hours ofharvest to eliminate any possible post harvest deterioration.

Gloss Measurements

The fruits were positioned in the glossmeter and illuminated by a lightbeam from a helium-neon laser at an angle of 60° to a planeperpendicular to the surface. A semi-conductive plate collected allreflected light from the surface of the fruits and a VCR camera (Sony,Japan), positioned directly facing the plate, recorded the images. Therecorded images were relayed to a computer, where they were analyzed bya specially designed computer program, which translated them into thecurvee form of light intensity (arbitrary units) Vs distance or lightscattering (pixels). With the curved surface glossmeter, a low valueindicated high gloss and vice-versa.

Gloss measurements for "Granny Smith" apples indicate that these werethe least glossy of the fruits examined, with measurements of 96.3pixels +/-4.8 obtained for the curved surface glossmeters.

EXAMPLE 3

Eggplants were examined. These are the most glossy of the fruitsexamined, with readings of 34.9 pixels +/-4.8 given by the curvedsurface glossmeters. It may be assumed that the very glossy appearanceof the eggplant is due to a very effective light scattering wax layercovering the peel.

Gloss measurements of the mature eggplants following wax extractionindicate that lack of wax results in a lower gloss. Results of 40.5pixels +/-1.8 were obtained using the curved surface glossmeters.

Mature green "Daniella 144" tomatoes exhibited curve gloss values of61.9 pixels +/-10.9, indicating they were slightly less glossy than theeggplant and yet more glossy than the apples.

EXAMPLE 4

Marble was polished to three different degrees of smoothness, and itsgloss was measured at each of these stages. Pronounced differences werefound between the three degrees of polish, which were assigned thevalues "glossy", "matte" and "semi-glossy".

                  TABLE 1                                                         ______________________________________                                        Types of gloss                                                                             Visual evaluation                                                                           Types of surfaces                                  ______________________________________                                        Specular gloss                                                                             Shininess, brilliance                                                                       medium-gloss surfaces                                                   of highlights                                                                               of book paper, paint,                                                         plastics, etc.                             Sheen                       Low-gloss surfaces ofg                                                                      paint, paper, etc.                  Contrast gloss or                                                                               Contrasst between                                                                          Low-gloss surfaces of                          luster                     textile fiber, yarnting                                                       and cloth, newsprint,as                                                                            bond paper, diffuse-                                                          finish metals, hair,                                                          fur, etc.                     Absence-of-bloom                                                                                 Absence of haze, or                                                                     High and semi gloss                              gloss                          surfaces in which                                                         reflected highlightscted                                                                 may be seen                             Distinctness-of image                                                                       Distinctness and                                                                                High-gloss surfaces                           gloss                        of all types in which                                                                      mirror images may be                                                          seen                                Surface-uniformity                                                                            Surface uniformity                                                                           Medium-to high-gloss                           gloss                        surfaces of all types                                                         nonuniformities as                                                            seen in textures                                 ______________________________________                                    

We claim:
 1. A glossmeter providing detailed information on the gloss ofan examined object, which comprises in combinationmeans for holding theobject with a substantial part of its surface exposed for examination,means for illuminating the object with a beam of light, and an array ofphotodetectors adapted to detect and measure light reflected anddiffused from the surface of the object, where there is provided anarray of photosensitive elements arranged at the inner surface of an arcdefining a quarter of a circle, the apex of which is at the axis of theobject and other end of which is located at the horizontal planesupporting the object, where means are provided for rotating the arcrespective the object by an angle from 90° to 360° respective theverticle axis.
 2. A glossmeter according to claim 1 where the lightsource is a laser, the beam of which can be directed at the objecteither at a fixed angle of incidence, or which can be directed at theobject at any predetermined angle between nearly horizontal and up toperpendicular with the supporting surface.
 3. A glossmeter providingdetailed information on the gloss of an examined object, which comprisesin combinationmeans for holding the object with a substantial part ofits surface exposed for examination, means for illuminating the objectwith a beam of light, and an array of photodetectors adapted to detectand measure light reflected and diffused from the surface of the object,where there are provided two arcs, of 180° each perpendicular with eachother, with an array of photosensitive elements adjacent each otherarranged on the surface of the arcs facing the object, means beingprovided for evaluating the signals from said elements, there beingprovided a laser for illuminating the object at an angle variable atwill, with a monochromatic beam of light.
 4. A glossmeter according toclaim 3 where the light source is a laser, the beam of which can bedirected at the object either at a fixed angle of incidence, or whichcan be directed at the object at any predetermined angle between nearlyhorizontal and up to perpendicular with the supporting surface.